Insects - friend or foe?

In an act of pure vandalism, possum has been at the roses again.  Partial to a Peony he sucks the tips of the not yet opened bud drawing out the moisture and making it almost impossible to bloom.  Then along comes this shiny beetle.  I never quite know with insects if there intentions are good - or not.  The aphids on the roses seem clearly bad, but the lady birds eat them so, that's good.  This shiny beetle was reflecting in the sun light making himself very obvious to all.  And given the amount of chooks and birdlife in my yard, I considered this to be a bit on the foolish side  but I'm sure it served some purpose.  The first year we moved in here we had a plague of grasshoppers.  As in biblical proportions.  They managed to eat everything we planted and even came indoors.  We could not get rid of them.  Then the chooks arrived.  No more grasshoppers.  They still enjoyed the odd nibble on the veggie patch but nothing as destructive as the grasshoppers.  The large blow flies as we call them are on steroids at the moment.  Pumped up and with full strength they hurl themselves at the windows.  I'm convinced they watch the back door and as soon as it's even slightly open, they whizz in.  Max loves to stalk them and will get close enough to them to pat them on the head.  Unfortunately that's about the best of his efforts.  He's doesn't like violence.  Insects can be interesting creatures and I'm sure there is much more to them than we know.  Except for spiders.  They're just plain evil.